1. Field of the Invention
The present invention generally relates to a projection system, and more particularly to a method and system for eliminating artifacts in overlapped projections.
2. Description of the Related Art
Recently, large display walls have been constructed using multiple projectors that each project their images onto a large screen. Typically, each projector in such a system provides parts of the image, thus composing the image from several xe2x80x9ctilesxe2x80x9d.
To avoid visible seams (e.g., discontinuities) in the composite image, projectors are typically arranged such that their projected images slightly overlap. Pixels in the overlapping areas are attenuated such that their relative contributions add up to 1. Thus, each projector provides a certain percentage (e.g., a relative contribution) of the final pixel color/intensity. Thus, ideally (e.g., in theory), such attenuation makes the overlap areas invisible to a viewer. That is, black pixels (e.g., having a value of 0) must be produced to avoid such discontinuities. Hence, imagine that in the overlap area, one projector provides 100 percent of the intensity. Then, the other projector must generate 0 percent intensity (i.e., an ideal black pixel). Such situation occurs at the edges of the overlap area (e.g., see FIG. 2)).
Unfortunately, xe2x80x9creal-worldxe2x80x9d (e.g., practical) projectors cannot produce perfectly black pixels. That is, although the input value for a given pixel may be 0, the projector still emits a small amount of light for those pixels. This is due, for example, to imperfections in the light valves used in liquid crystal display (LCD) projectors or residual phosphorescence in cathode ray tube (CRT) projectors.
As a result of such projections, seams are visible where the xe2x80x9ctilesxe2x80x9d (e.g., images) generated by different projectors overlap. Such seams are visually distracting and can potentially convey information to the viewer that is not part of the image but purely an artifact of the overlapping tiles.
FIG. 1 illustrates a concrete example of the above-mentioned problem. That is, a conventional system uses multiple projectors 101-106 that project their respective images 107-112 onto a common projection screen 100. These images 107-112 are also referred to as xe2x80x9ctilesxe2x80x9d. Separate processors/computers 113-118 provide the pixel information to each of the projectors. Computers 113-118 can be totally independent of each other, or can be in communication with each other over a network, or can be connected to a central controller that determines their operation.
To ease registration of the tiles, the tiles produced by the projectors typically overlap. Depending on the number of projectors and their overlap, this creates areas that are illuminated by one, two or four projectors 119-121. Each projector modulates the intensities of the pixels in the overlap areas, in order to provide a smooth transition between pixels provided by the contributing projectors.
FIG. 2 illustrates two out of many possible blending functions (e.g., linear roll-off and cosine-square roll-off). For pixels in the overlap area, the pixel value is multiplied by the blending function. As can be seen from FIG. 2, the blending functions used by neighboring projectors add up to 1, thus creating the visual impression of a smooth transition between tiles.
FIG. 3 shows an example of pixels positioned along a scanline. The graph 301 shows the computed pixel intensities for the scanline. Graphs 302 and 303 illustrate the pixel intensities after ideal modulation with the blending functions for the two projectors. Finally, graph 304 shows the sum of the modulated pixels. The sum of the modulated pixels is the same as the computed pixel values.
FIG. 4 shows the relationship between the specified pixel value and the displayed intensity (e.g., computed value vs. actual/real displayed value). Graph 401 shows an ideal mapping of pixel values to intensities, which graph 402 shows a more realistic mapping. It is noted that even an input pixel value of 0 results in a non-zero intensity on the display. Further, real mappings from pixel values to intensities also are frequently non-linear.
FIG. 5 shows the non-ideal case. FIG. 501 shows again the computed pixel intensities for the scanline. Graphs 502 and 503 show the effect of a non-perfect display of black pixels (e.g., even black pixels have some non-zero intensity in that pixel intensities will not assume a value of 0 in spite of a blending function value of 0. That is, the pixels do not assume a value of 0 because of the imperfection in the projector (e.g., leaking liquid crystal displays (LCDs) or persistence of phosphor in CRTs). Graph 504 shows the effect of summing up the modulated pixel values. It is noted that the pixel intensities in the overlap area are too large, thereby creating the effect of visible seams in the composite image.
Thus, hitherto the present invention, the conventional systems suffer from the problem of producing visible seams which is annoying and in which the viewer may be given wrong information as a result of such increased intensity.
In view of the foregoing and other problems of the conventional methods and structures, an object of the present invention is to provide a method and structure in which the artifacts such as seams are eliminated.
In a first aspect of the invention, a method of eliminating visible artifacts in overlapped projections produced by a plurality of projectors, includes in areas outside of the overlap areas, raising an intensity of first predetermined color pixels to match a level of the first predetermined color in the overlap areas, and scaling values of second predetermined color pixels in the overlap areas such that the values do not exceed the maximum pixel value of a single projector of the plurality of projectors.
In a second aspect of the present invention, a projection system includes a display screen, a plurality of projectors each for producing a respective image portion for being displayed on the screen, a plurality of image portions forming a composite image having a plurality of pixels, the plurality of image portions having overlapping image areas, and means, coupled to the projectors, for adjusting an intensity of predetermined ones of the pixels across the screen to achieve uniform intensity of the predetermined pixels.
In another aspect of the present invention, a signal-bearing medium incorporating the inventive method is provided.
With the unique and unobvious features of the invention, visible seams and artifacts are efficiently and reliably eliminated. Further, while the invention can be implemented in a combination of software and hardware, the present invention also may be advantageously implemented in software only. Thus, in such a case, the present invention would not require any additional hardware.